This invention relates to an aircraft control system and more particularly to a system for computing a yaw compensated angle of attack.
Modern commercial aircraft typically include a stall warning system which is triggered by the angle of attack of the aircraft as determined by an angle of attack vane. Such aircraft also include an integrated airspeed control, command and display system which aid a pilot during take-off, climb out, let down, approach, landing and go-around maneuvers. Such integrated systems are also based on various parameters relating to flight conditions including the aircraft's angle of attack as determined by an angle of attack vane.
It is customary to locate these angle of attack vanes on the sides of an aircraft's fuselage. However, these side mountings may lead to a problem when the aircraft is flown in yawed flight. As used herein, the term "yaw" refers to the condition of an aircraft when the longitudinal axis of the aircraft is angled to the left or right of the direction of flight. Thus, the yaw angle or side slip angle refers to the angular difference between the aircraft's heading and the aircraft's direction of flight. Under such circumstances, i.e., when an aircraft is flown in a yawed condition, the position of the angle of attack sensing vane will be determined by the local air flow passing the vane. The angle of attack vanes are usually located so that the changes in the local air flow at the vane cause the vane to pivot in accordance with the angle of attack. The local air flow at these fuselage locations are determined to a lesser extent by the yaw of the aircraft so that the indicated angle of attack is actually a function of both the angle of attack and the yaw.
In order to overcome the problem associated with yaw, a yaw vane has been used to supply a correction factor. A yaw vane is a movable vane, similar to an angle of attack vane, but which is typically mounted on the outside of the fuselage along the aircraft's centerline. The vane is mounted for rotation about the aircraft's vertical axis so as to align with the airflow past the aircraft. Thus, the change in position of the vane when the aircraft enters a yaw condition is proportional to the sideslip angle. However, the addition of a yaw vane on the exterior of an aircraft is undesirable and is complicated because of location, icing, reliability and cost. Furthermore, it is difficult to find locations for dual installations of a yaw vane on the exterior of an aircraft.
Therefore, there appears to be a need in the aircraft control art for an improved control system which provides a yaw compensated angle of attack signal and at the same time eliminates any need for an externally mounted yaw vane.